Field of the Invention
The present invention relates to a wireless local area network (WLAN) system, and more particularly, to a method of transmitting and receiving a packet on the basis of a multiple input multiple output (MIMO) transmission scheme by an access point (AP) and a station (STA).
Discussion of the Related Art
With the advancement of information communication technologies, various wireless communication technologies have recently been developed. Among the wireless communication technologies, a wireless local area network (WLAN) is a technology whereby Internet access is possible in a wireless fashion in homes or businesses or in a region providing a specific service by using a portable terminal such as a personal digital assistant (PDA), a laptop computer, a portable multimedia player (PMP), etc.
The IEEE 802.11n is a technical standard relatively recently introduced to overcome a limited data rate which has been considered as a drawback in the WLAN. The IEEE 802.11n is devised to increase network speed and reliability and to extend an operational distance of a wireless network. More specifically, the IEEE 802.11n supports a high throughput (HT), i.e., a data processing rate of up to above 540 Mbps, and is based on a multiple input and multiple output (MIMO) technique which uses multiple antennas in both a transmitter and a receiver to minimize a transmission error and to optimize a data rate.
With the widespread use of the WLAN and the diversification of applications using the WLAN, there is a recent demand for a new WLAN system to support a higher throughput than a data processing rate supported by the IEEE 802.11n. A next-generation WLAN system supporting a very high throughput (VHT) is a next version of the IEEE 802.11n WLAN system, and is one of IEEE 802.11 WLAN systems which have recently been proposed to support a data processing rate of above 1 Gbps in a MAC service access point (SAP).
To effectively utilize a radio channel, the next-generation WLAN system supports multi user-multiple input multiple output (MU-MIMO) transmission in which a plurality of non-access point (AP) stations (STAs) concurrently access to a channel. According to the MU-MIMO transmission, an AP can transmit a frame concurrently to one or more MIMO-paired STAs.
As an encoding scheme, binary convolutional coding (BCC) and low density parity check (LDPC) encoding are provided in a WLAN system. Since data transmission and reception between an AP and an STA have a one-to-one relation in a legacy WLAN system and a WLAN system supporting a high throughput, it has been enough to attach information related to an encoding scheme of encoded data to a packet to be transmitted. However, a next generation WLAN system may have a different encoding scheme of a data sequence to be transmitted to each STA since the AP can transmit packets simultaneously to a plurality of STAs by using a MU-MIMO transmission scheme.
The AP may have a different a modulation and coding scheme (MCS) to be signaled according to a situation where SU-MIMO transmission is achieved to a specific STA or a situation where MU-MIMO transmission is achieved to a plurality of STAs. In case of the SU-MIMO transmission, an MCS index is signaled to a specific STA. However, in case of the MU-MIMO transmission, respective MCS indices need to be signaled to a plurality of MU-MIMO paired STAs. Therefore, there is a need for a method of transmitting and receiving a packet by considering a MIMO transmission scheme of an AP and a capability of a transmission target STA in a next generation WLAN system.